Touch screens are used in conjunction with a variety of display types, including cathode ray tubes (e.g., CRTs) and liquid crystal display screens (e.g., LCD screens), as a means of inputting information into a computer system. When placed over a display, the touch screen allows a user to select a displayed icon or element by touching the screen in a location that corresponds to the desired icon or element. Touch screens are becoming more prevalent data input interfaces as computers and other electronic devices become more ubiquitous. For example, touch screens may now be found in workshops, warehouses, manufacturing facilities, restaurants, on hand-held personal digital assistants, automatic teller machines, casino game-machines, and the like.
One type of touch screen, a capacitive touch screen, includes a capacitive sensor circuit with multiple sensor bars that each produce an electric field. Often, but not necessarily, the sensor circuit is laminated with an optically transparent protective substance, such as a glass pane. A touch in proximity of one or more of the sensor bars modulates the electric field and creates a signal. The signal passes from the sensor bars to a controller using a network of lead lines that electrically connect the sensor circuit to the controller. The controller resolves the signal or signals to determine the location of the touch on the screen. The X-Y coordinates of the location may then be communicated to another processor for further processing, such as to a computer for entering an order of an item displayed and selected on the screen.
The architecture of the conventional capacitive touch sensor affects the ability to accurately resolve the location of a touch. Conventionally, each lead line that connects the sensor bars to the controller is connected to multiple sensor bars. For that reason, a signal on a lead line can be indicative of a touch on more than a single sensor bar. Conventional touch sensor designs employ connection layouts that allow a comparison of signals present on lead lines of one side to signals on lead lines of the other side. The comparison allows the controller to resolve which of multiple sensor bars actually experienced the touch. In other words, the conventional touch sensor couples a different set of lead lines to each side of the sensor bars so that signals present on one side of the touch sensor in conjunction with signals present on the other side together uniquely define each sensor bar.
Touch screen designers are faced with the problem of designing touch screens and sensor circuits that are economical to manufacture and that will accurately establish the touch location.